Two-dimensional portraits represented by photographs have gained widespread acceptance and are now established. General photographs can be easily taken with a camera, and development-and-printing service can also be received at a low price. Memorial photographs can be taken in a photo studio, and they can be obtained as photographs of extremely high quality. So it can be said that customer satisfaction with such photographs already reaches a sufficiently high level.
On the other hand, it is hard to say as of this point in time that stereoscopic portraits viewed as three-dimensional images are widely accepted. For establishment of stereoscopic pictures, it is necessary to make stereoscopic portraits meeting customer requirements, not standardized copies of the same picture, available to customers at low prices. For instance, it is anticipated that stereoscopic portraits viewed as three-dimensional images will be more widely accepted and established than two-dimensional pictures so long as stereoscopic portraits of high quality can be delivered to customers at high speed and low prices.
A high-quality three-dimensional image in portrait taking can be obtained through a holographic stereogram, or a hologram. The holographic stereogram, however, requires multiple interference exposures, so it takes too long a time to get one sheet of picture. As a result, it becomes difficult to get a high-quality picture at a low price.
Holography for portrait taking is carried out using pulsed lasers (See, e.g., LEONARDO, 1992, Vol. 5, No. 5, pp. 443–448).
Holograms formed using pulsed lasers in portrait taking can be converted into reflection form and reproduced with white light, whereby it becomes possible to enjoy viewing the portraits taken as three-dimensional images. Generalization of such a holographic technology, however, faces a big problem that the images obtained are basically monochromatic black-and-white images in addition to the price problem mentioned above. Although the color seen actually can be modified variously by processing, there are many cases where the portraits obtained look weird because they are monochrome photographs. While full-color holograms can be obtained in principle by using pulsed lasers corresponding to three colors, blue, green and red ones, they require a large-scale taking system, including apparatus.
Further, the holograms formed using those pulsed lasers in portrait taking are copied from transmission form to reflection form without a change in image magnification to result in furtherance of the weirdness as mentioned above. These points cause stumbling blocks to generalization of stereoscopic portraits viewed as three-dimensional images in addition to the problem of being expensive.
Various recording methods have been proposed for photosensitive materials used in wavefront recordings of interference waves, or holography, and they are in actual use. Representatives of photosensitive materials known to be usable in holography are silver halide photosensitive materials, dichromated gelatin photosensitive materials, photoresist materials, photopolymer materials and thermoplastic photosensitive materials. Of these materials, silver halide photosensitive materials feature their high sensitivities, and they are widely used in areas of various types of displays and in the field of researches. More specifically, further sensitization of silver halide photosensitive materials can be utilized for reducing the quantity of laser light used and shortening an exposure time, and can lead to simplification and facilitation of wavefront recordings. Accordingly, even further sensitization of silver halide photosensitive materials for use in holography is a welcome trend in wavefront recordings of interference waves (See, e.g., JP-A-10-123643).
However, silver halide emulsion particles incorporated in a silver halide photosensitive material for use in holography are required to be superfine particles having projected area diameters of 100 nm or less, so there are cases where techniques for sensitization of silver halide emulsion particles for use in general photography are inapplicable just as they are. Conversely, there are cases where techniques inapplicable to silver halide emulsion particles for general photography can serve as techniques to sensitize such superfine particles. On the whole, concurrent performance of gold sensitization and reduction sensitization is forbidden to silver halide emulsion particles hitherto used in photography (See, e.g., JP-A-5-181238). More specifically, while each of gold sensitization and reduction sensitization individually has sensitizing effect, concurrent use of these two sensitization methods causes an increase in fog and deterioration in keeping quality, and makes it impossible to exploit each individual full potential.
In addition, sensitized superfine particles are unstable because their sizes are extremely small, and readily increase in size. And ripening of superfine particles proceeds with the lapse of time during a period from preparation of the silver halide emulsion particles to coating thereof, so silver halide emulsion particles are required to be coated immediately after preparation in some cases. Accordingly, it is unsuccessful yet to produce a holographic silver halide photosensitive material with high reproducibility and high stability by simultaneously coating two or more types of silver halide emulsion particles so as to have a multilayer structure.
Furthermore, since it is exposed to laser light, the silver halide photosensitive material is, in general, spectrally sensitized at the wavelength corresponding to the laser light. Spectral sensitizing dyes suitable for such spectral sensitization are disclosed (See, e.g., JP-A-10-149084).
In addition, spectral sensitization with two types of spectral sensitizing dyes suitable for a holographic photosensitive material used in producing a multicolor hologram is disclosed (See, e.g., JP-A-3-203765).
However, these disclosed sensitization methods are lacking in universal applicability for all wavelengths of generally used typical lasers. More specifically, it is impossible for one sheet of photosensitive material to simultaneously satisfy high sensitivities characteristic thereof to all wavelengths of typical lasers, including the wavelength of 694 nm at which ruby laser operates, the wavelength of 647 nm at which krypton laser operates, the wavelength of 633 nm at which helium-neon laser operates, the wavelength of 532 nm at which YAG laser operates and the wavelengths of 515 nm and 488 nm at which argon laser operates. Such being the case, no sensitive material having high sensitivity to all of typical lasers, or no general-purpose photosensitive material, is found yet.
A silver halide photosensitive material is exposed to laser light, and thereon interference fringes of width narrower than the wavelength of the laser light are recorded. The recorded interference fringes are sensitive to processing of the silver halide photosensitive material. When the silver halide photosensitive material shrinks in thickness at the time of processing, compared with the time of exposure, the wavelength of reproducing light is generally shifted to a shorter wavelength than that of the recording light. This is because the space between interference fringes becomes narrower at the time of processing than at the time of exposure. On the other hand, when the silver halide photosensitive material extends in thickness at the time of processing, compared with the time of exposure, the wavelength of reproducing light is generally shifted to a longer wavelength than that of the recording light. This is because the space between interference fringes becomes wider at the time of processing than at the time of exposure. These shifting of wavelengths are generally conducted by devising pre-treatment or after-treatment of the silver halide photosensitive material. However, these methods give rise to variations in recording characteristics and reproduction characteristics, and make the handling even more inconvenient.
With the intention of circumventing these problems, the art of incorporating the function of controlling a thickness change at after-treatment time into a silver halide photosensitive material itself is disclosed (See, e.g., European Patent No. 240,466).
Further, the sensitive material including two layers having different shrinkage factors at after-treatment time is disclosed (See, e.g., EP-A-241418).
In these disclosed methods, however, there is trouble that the silver halide photosensitive materials suffer degradation in recording characteristics because additives unnecessary to their sensitivity are added. Moreover, the reproduction characteristics are determined near uniquely and cannot be controlled freely by after-treatment. With this being the situation, there is not yet any art of producing holographic silver halide photosensitive materials which are excellent in interference pattern-recording characteristics and provided with freely controllable reproduction characteristics.